EFFICIENT REGULARIZED PROXIMAL QUASI/NEWTON METHODS FOR LARGE-SCALE NONCONVEX COMPOSITE OPTIMIZATION PROBLEMS

Optimization problems with composite functions consist of an objective function which is the sum of a smooth and a (convex) nonsmooth term. This particular structure is exploited by the class of proximal gradient methods and some of their generalizations like proximal Newton and quasi-Newton methods. In this paper, we propose a regularized proximal quasi-Newton method whose main features are: (a) the method is globally convergent to stationary points, (b) the globalization is controlled by a regularization parameter, no line search is required, (c) the method can be implemented very efficiently based on a simple observation which combines recent ideas for the computation of quasi-Newton proximity operators and compact representations of limited-memory quasi-Newton updates. Numerical examples for the solution of convex and nonconvex composite optimization problems indicate that the method outperforms several existing methods.